1. Field of the Invention
The present invention relates generally to resilient surface coverings and, more particularly, to a resilient floor covering having a wear surface which provides improved stain, mar, scuff, and soil resistance and to a method for making the same. The present invention additionally relates to a resilient floor covering having an improved strengthening layer and to a method for making the same.
2. Description of Related Art
Resilient surface coverings, and in particular resilient floor coverings, are well known in the art. In the manufacture of resilient floor coverings, normally, a relatively flat base layer or substrate is laid out in substantially horizontal condition. Such a base layer or substrate is usually a felted or matted fibrous sheet of overlapping, intertwined filaments and/or fibers, usually of asbestos or of natural, synthetic or man-made cellulosic origin, such as cotton or rayon, although many other forms of sheets, films, textile materials, fabrics or the like, may be used.
Upon this substantially flat, horizontally positioned base layer or substrate is then deposited or applied a substantially uniform layer of a liquid or semi-liquid resinous composition which contains a synthetic polymeric material, usually an ungelled polyvinyl chloride plastisol and normally containing a blowing or foaming agent. This liquid or semi-liquid plastisol vinyl resin composition is subsequently firmed or gelled at an elevated temperature to a relatively more stable condition by procedures which are conventional and well-known in the art. This relatively firm, gelled plastisol may then be printed with a decorative, multicolored pattern or design in which certain predetermined areas may contain a blowing or foaming inhibitor which subsequently modifies or alters the action of the blowing or foaming agent in those certain predetermined areas. Several different printing ink compositions may be used in such procedures.
Typically, a wear layer is then applied to the surface of the polyvinyl chloride plastisol. Generally, the wear layer consists of either a plasticized polyvinyl chloride composition and/or a urethane or urethane acrylate composition. Examples of such wear layers can be found in, for example, U.S. Pat. No. 4,333,987 to Kwart et al., U.S. Pat. No. 4,180,615 to Bettoli, U.S. Pat. No. 4,393,187 to Boba et al., and U.S. Pat. No. 4,507,188 to Chu.
An optimum resilient floor covering should be stain, mar, scuff, and soil resistant but must also be flexible. Those in the art have had to sacrifice some of these properties in achieving one or more of stain, mar, scuff or soil resistance or flexibility.
The term "mar resistance" refers to the ability of the wear surface to resist scratching, which results in a loss of gloss due to abrasive wear. Good mar resistance results in good gloss retention.
"Stain resistance" generally refers to the ability of the wear surface to resist stains from foods, chemicals, etc., that a flooring wear surface may be subjected to through normal household use.
The term "scuff resistance" is the ability of the wear surface to resist plastic flow when subjected to the force and frictional heat caused by the dragging of, for example, rubber or plastic soled shoes.
"Soil resistance" is the ability of the wear surface to resist becoming discolored through staining, scratching, scuffing or other degradation mechanisms.
Hard wear surfaces generally are very stain resistant. But because it is desired to achieve a resilient flooring product that is flexible, the wear surface must be flexible enough to meet product requirements during manufacture, transportation, installation and final use. Wear surfaces which exhibit the best stain resistant properties are too hard, and cannot meet the flexibility requirements of a resilient flooring product, especially when applied at dry film thickness (DFT) greater than 1 mil. Wear surfaces for coated PVC resilient floor coverings are typically greater than about 1 mil. Flexible wear surfaces generally have better mar resistance than hard wear surfaces but do not have as good stain resistance as hard wear surfaces.
Because hard coatings could not be used due to the flexibility requirement, the wear surface was made "tougher" and more "elastic" to achieve good mar resistance. Unfortunately, these "elastic" formulations exhibit marginal stain resistance.
Thermoplastic wear surfaces, such as plasticized non-cross-linked polyvinyl chloride wear surfaces, have better stain resistance than most thermoset urethanes but do not have the ability of thermoset wear surfaces, such as chemically cross-linked urethane or urethane acrylate wear surfaces, to resist marring, scuffing and/or soiling resistance.
In recent years the art has tried to bridge the gap between mar and stain resistance. Because neither plasticized polyvinyl chloride wear surfaces nor urethane or urethane-acrylate wear surfaces have been found to possess all of the desired resistance properties, considerable effort has been expended to develop new and different types of wear layers. Some participants in the resilient flooring industry have attempted to circumvent the problems of hard polyurethane coatings by using coatings made from other polymers.
In U.S. Pat. No. 4,781,987 to Bolgiano et al., there is disclosed a resilient floor covering that is alleged to have improved scratch and stain resistance. The resilient floor covering includes a resilient support surface and a resilient wear surface bonded to the support surface, the wear surface comprising a top first layer material and a cross-linked underlying second layer material selected from the group consisting of a moisture cured polyurethane, a moisture and UV-cured polyurethane, a UV-cured polyurethane and a cured unsaturated polyester adhered to the support surface, the first layer material being obtained from the thermal curing of a composition comprising a polyol component, an aminoplast component, and an acid catalyst component, wherein the first layer material conforms to physical deformations of the cross-linked second layer material and having improved scratch and stain resistance properties relative to the cross-linked second layer material. One commercially-practiced example corresponding to this disclosure uses an aminoplast of a type similar to that which is customarily used as a component of the protective barrier coating on the inside surfaces of food and beverage cans.
However, the aminoplast resin coating of Bolgiano et al. '987 suffers from several deficiencies. The gloss level is typically lower than that of polyurethane coatings, gloss retention is typically poorer than polyurethane coatings and, in some applications, the aminoplast coating may be removed by a scuffing type impact. Moreover, the Bolgiano et al. coatings require the expenditure of additional energy to evaporate the water or organic solvent. Thus, the only advantage of the aminoplast resin coating is for providing stain resistance.
Tough and rubbery polyurethane coatings have excellent gloss retention but have relatively poor stain resistance. Hard polyurethane coatings have excellent or at least very good resistance to staining.
These same hard polyurethane coatings are relatively brittle and tend to crack when applied over a flexible vinyl floor covering at any thickness approaching the usual and customary thickness for polyurethane coatings on this substrate. The brittleness problem with these hard polyurethane coatings can be circumvented by very thin application, such as 10% of the usual and customary dry film thickness. Although the very thin dry film thickness of a hard polyurethane coating on a flexible vinyl floor covering has a very good adhesion as measured by tests such as a crosshatch adhesion, the thin coating can be removed from the vinyl substrate by a scuffing type of impact.
Applicants have unexpectedly discovered that the disadvantages of the tough and rubbery coatings and the hard polyurethane coatings can be overcome by utilizing a two layered wear layer of the instant invention. The resulting coated resilient flooring product is stain, mar, scuff, and soil resistant and flexible and retains the typical polyurethane high gloss level.
The prior art has additionally searched for a strengthening layer utilized underneath of the foamed layer that adds toughness to a resilient floor covering. A strengthening layer for a resilient floor covering should have the advantageous properties of cut, tear and deformation resistance during installation and resistance to indentation and gouging during use. Generally, prior art strengthening layers of fibrous sheets or resin impregnated fibrous sheets are used. However, the prior art strengthening layers typically suffer from the disadvantages of deformation and tearing during installation and/or poor indentation resistance during use.
U.S. Pat. No. 3,870,591 to Witman discloses an intermediate, fluid-applied, cross-linked, reinforcing layer which is flexible and resistant to stretching and which stabilizes the floor covering during use. This strengthening layer is disposed between two foam layers.
Applicants have unexpectedly discovered that this intermediate layer can be advantageously utilized underneath the foam layer or underneath all of the foam layers if more than one foam layer is present to strengthen a resilient floor covering. Moreover, the cross-linked strengthening layer has improved strength, toughness, resistance to breakage, especially resistance to tearing, and resistance to deformation, especially resistance to indentation and sliding gouging, when compared to a conventional, vinyl backed layer.